Older age is an assumed risk factor for the development of gestational diabetes mellitus (GDM) in women. Here, we studied the effect of age and pregnancy on fat mass and glucose tolerance in rats. We performed intravenous glucose tolerance tests (IVGTTs) in 3- and 9-month-old rats, either nonpregnant or pregnant (day 20). In addition, we measured maternal fat mass, by dual-energy x-ray absorptiometry, and plasma leptin and lipid levels, as well as fetal parameters, on day 22. Nine-month-old rats had higher fat mass and plasma leptin, cholesterol, and triglyceride concentrations than 3-month-old rats. Glucose levels during the IVGTTs were elevated at several time points in 9-month-old rats, and the area under the curve (AUC) was increased. Pregnancy did not affect fat mass or the AUC for glucose during the IVGTT. The AUC for insulin during the IVGTTs was increased by age as well as pregnancy, but there was no interaction between the two by 2-factor analysis of variance. Reproductive performance was less optimal in 9-month-old rats, with a reduction of individual fetal and placental weight. In conclusion, 9-month-old rats exhibit a deterioration in glucose tolerance, possibly linked to the age-dependent increase in fat mass and leptin concentrations. Pregnancy also comprises certain adaptations in lipid and glucose metabolism, but because no interaction was found between both factors, the effect of pregnancy is not aggravated by aging. This may suggest than an increased gestational diabetes mellitus prevalence in older women can similarly be explained by age as such.